1. Field of the Invention
The present invention relates generally to a handpiece for a dental instrument and more specifically to a dental air-abrading tool used for etching or roughening hard dental surfaces such as metals, porcelains or composites, to increase the surface area to which adhesive composites are applied and thereby to dramatically improve bond strength.
2. Description of the Prior Art
Use of small etching tools that are hand operated is well known in the dental industry where preparation of artificial dental substrates is often required for repair and cementing procedures. Such tools operate by directing a gaseous stream mixed with an abrasive material to the surface to be prepared. The gaseous medium, (often compressed air), and small solid particles comprising the abrasive material are supplied to the tool and are mixed so that the abrasive material becomes entrained within the gaseous medium. The mixture is then discharged through a nozzle upon activation of the tool by the operator. Numerous types of these instruments are available on the market and are generally in the form of a hand-held device with various combinations of internal components.
For example, U.S. Pat. No. 4,941,298 to Fernwood et al., discloses an apparatus for abrading surfaces through mechanical sandblasting principles using a jet stream containing a mixture of solid particles and compressed air. The apparatus comprises a hollow tubular handle with a nozzle at one end for dispensing the mixture and a member at the other end for receiving the compressed air and solid particles. Within the hollow tubular handle are flexible tubes which individually carry the compressed air and the solid particles to a mixing chamber located within the nozzle. A pinch lever is also provided to inhibit the compressed air flow by compressing the air supply tube in the stand-by mode of the tool. The tool is activated by depressing a button which releases the pinch lever and allows the supply tube to return to its original shape thereby releasing the blockage of the air supply. When the button is released, the pinch lever returns to its original position and compresses the air supply tube again. This type of activating button has the disadvantage that when the button is pushed, the tip of the device tends to jerk a bit. As a result, the operator may spray abrasive where it is not desired.
U.S. Pat. No. 4,648,840 to Conger, Sr., discloses a dental polisher having a pair of conduits concentrically arranged within the polisher's body for providing flows of abrasive material and fluid. The conduits extend into a nozzle for discharging and directing the flow to a surface. Other conventional devices are shown in U.S. Pat. No. 4,776,794 to Meller, U.S. Pat. No. 5,199,229 to Herold et al., and U.S. Pat. No. 4,950,160 to Karst, each disclosing similar instruments comprising combinations of internal tubes, pipes, conduits, etc.
A common drawback to the above mentioned instruments is that in most instances the combination of flexible tubes, pipes and other internal components are difficult to install within the instrument resulting in high costs of manufacture. Also, with instruments operated by the constant compressing and releasing of flexible tubing the problem of deterioration of the tubing and eventual leakage arises. These type of instruments are prone to clogging and are often difficult to clean. Since the internal flexible tubes are not necessarily made of high temperature materials, it may not be possible to sterilize the body of the instrument using a standard autoclave. Sterilizing just the nozzle of conventional devices may not be enough to prevent cross-infection. Accordingly, it would be advantageous to provide a handpiece for a dental instrument which is easy to manufacture, reliable in operation, easy to clean and fully sterilizable by autoclaving.